Heretofore, image forming apparatuses using electrophotography or electrostatic printing use a belt conveyance device having an endless belt (hereinafter also referred to simply as “belt”) suspended around multiple suspending rollers. The belt is used as a conveyance member that bears and conveys toner images, bears and conveys recording material on which a toner image is formed, and so forth. Types of conveyance members that bear and convey toner images include a belt-shaped electrophotographic photosensitive member (photosensitive belt), an intermediate transfer member (intermediate transfer belt) that bears and conveys a toner image transferred from a photosensitive member for transfer onto recording material, and so forth. Types of conveyance members that bear and convey recording material on which a toner image is formed include a recording material bearing member (conveyance belt) that bears and conveys recording material onto which a toner image is transferred from a photosensitive member, and so forth.
An example of an electrophotographic image forming apparatus having an intermediate transfer belt will be further described. A general problem with an intermediate transfer belt suspended around multiple suspending rollers and rotationally driven (conveyed) is “belt deviation” where the belt is deviated to one end side or the other in the width direction when being driven. This belt deviation occurs due to outer diameter precision of the suspending rollers, alignment precision among the suspending rollers, and so forth.
One measure to deal with this belt deviation is a method called “active steering”, where at least one suspending roller is inclined as to another suspending roller, thereby moving the intermediate transfer belt in the opposite direction as to the displacement of the intermediate transfer belt in the width direction.
Japanese Patent Laid-Open Nos. 2010-223981 and 2002-2999 describe a configuration where a frame supporting a steering roller can be inclined as to a frame supporting another suspending roller, and one end of the frame supporting the steering roller is raised/lowered along an edge of the frame supporting another suspending roller.
Japanese Patent Laid-Open No. 2000-264479 describes a configuration where one end of a rotation shaft of a steering roller is supported by a steering arm that is capable of rocking, and the other end is supported by a fixed arm, with the one end of the rotation shaft of the steering roller being raised/lowered by the steering arm.
However, the configuration where the frame supporting the steering roller is raised/lowered along the edge of the other frame, as described in Japanese Patent Laid-Open Nos. 2010-223981 and 2002-2999, readily exhibits positional deviation of the steering roller in a direction generally orthogonal to the steering direction, due to looseness and wear at a guide portion. Also, in the configuration described in Japanese Patent Laid-Open Nos. 2010-223981 and 2002-2999, the greater the distance from the center of rotation of the steering roller to a slide face between the frames is, the more readily the frame is inclined with the support point as the point of origin, due to tension of the intermediate transfer belt, and the weight of the steering roller itself. Accordingly, the steering roller is prone to sagging greatly. As a result, even in a state where the steering roller should be maintained in parallel to another suspending roller, the position of the one end of the steering roller easily deviates, leading to misalignment with the other suspending roller, and belt deviation readily occurs.
In comparison, the configuration where the ends of the rotation shaft of the steering roller are supported as described in Japanese Patent Laid-Open No. 2000-264479 is advantageous with regard to the point of misalignment of the steering roller described above. However, the configuration described in Japanese Patent Laid-Open No. 2000-264479 involves twisting the fixing arm when inclining the steering roller. Accordingly, the center of twisting of the fixing arm is the actual center of inclination of the steering roller. In this case, the position of the center of inclination will differ depending on the shape of the fixing arm, and it is difficult to set the center of inclination of the steering roller at a desired position. Consequently, the perceived amount of positional deviation, where the position of the edge portion of the intermediate transfer belt is perceived to move in the width direction without moving over the steering roller, due to inclination of the intermediate transfer belt along with the inclination of the steering roller, increases. In a configuration where a sensor that detects the position of the intermediate transfer belt in the width direction inclines along with the steering roller, this results in positional deviation of the intermediate transfer belt that is not detected by the sensor. In a configuration where the sensor is not inclined along with the steering roller, the perceived positional deviation is added to the amount of positional deviation due to belt deviation and output, which is undesirable in performing highly-precise positional control of the intermediate transfer belt.
Although description has been made above by way of an example of an intermediate transfer belt, the same problem can occur in any belt conveyance device having a steering mechanism such as described above.